Small angle neutron scattering study of magnetic length scales in disordered ferromagnetic Ni-V alloys.

We used small angle neutron scattering (SANS) to reveal magnetic microstructures in a disordered ferromagnet (FM) close to quantum critical point (QCP) where long range order is suppressed with critical temperatures Tc approaching zero. First results of the alloy Ni-V with low Tc are presented on well characterized polycrystalline samples that demonstrated the quantum Griffiths phase signatures for “random” magnetic inhomogeneities [1]. SANS data were collected at NG7SANS, NIST. Full polarization analysis was effective to resolve weak magnetic scattering from dominating nuclear scattering. Angular dependent spin-flip scattering identified magnetic short-range clusters. Angular dependent non-spin-flip interference term recognized long-range magnetic domain contributions. The disordered FM Ni-V presents short-range correlations coexisting with long-range correlations at low temperatures well below Tc in the quantum Griffiths regime close to the QCP.
[1] R. Wang et al, Phys. Rev. Lett. 118, 267202 (2017)